The invention relates to a pneumatic brake booster for a motor vehicle having a control valve with offset intake and equalizing valve seats.
The invention relates more particularly to a pneumatic brake booster for a motor vehicle, of the type comprising a rigid casing inside which there can move a transverse partition sealingly delimiting a front chamber, subjected to a first pressure, and a rear chamber subjected to a second pressure that varies between the first pressure and a pressure higher than the first pressure, which is able to act on an actuating rod of a master cylinder associated with the booster by way of a reaction disk, of the type which comprises a tubular moving piston which is slideably mounted in the casing and which is secured to the moving partition, of the type which comprises a control rod moving in the piston selectively according to an axial input force exerted forward against the action of a return force exerted on the rod via a return spring, of the type in which the movements of the control rod are able to determine the openings and closings of at least one axial intake valve which is inserted between a pressure source subjected to the pressure higher than the first pressure and the rear chamber, and of at least one axial equalizing valve which is inserted between the front chamber and the rear chamber, to actuate the moving partition, and of the type in which a plunger, passing through the moving partition and secured to the end of the control rod, is able to act directly upon the actuating rod of the master cylinder by way of the reaction disk.
Numerous examples of conventional boosters of this type are known.
In such a booster, the piston is secured to the moving wall. It is, for example, fitted through the moving partition. Furthermore, the equalizing valve and the intake valve form part of a single three-way valve a common seat of which is formed of a stepped front face of a moving element which is elastically returned against a flange of the plunger and against a flange of the piston from which flanges it can be selectively separated in order to open the equalizing valve or the intake valve.
Thus, a roughly radial duct which passes through the piston and which opens into the front chamber and a roughly axial duct which opens to the outside of the booster can be placed selectively in communication by way of one of the valves with a radial duct which passes through the piston and which opens into the rear chamber in order to maintain or cancel a pressure difference between the rear chambers and cause the moving partition to move.
Such a design has the disadvantage of entailing ducts made in the piston with complex shapes, which disturb the air flow. As a result, a booster produced according to this design generally has relatively high response times and proves noisy.
Furthermore, such a design is particularly expensive to implement because it entails the use of a piston whose interior shapes, intended to form the ducts, can be produced only by a machining method.
The invention proposes a design which allows these disadvantages to be remedied and in which the ducts are axial and form part of various tubular elements of the booster. This design encourages the air to flow through the valves, and this makes it possible to reduce the booster response times while at the same time giving it quiet operation. What is more, this new design allows most of the booster elements to be made using a pressing method which is less expensive than the conventional machining methods.
To this end, the invention proposes a booster of the aforementioned type, characterized in that it comprises:
a floating tubular element external to the plunger, which is axially mobile and which is elastically returned toward the moving partition, of which axially offset transverse faces have first sealing elements for the axial intake and equalizing valves,
a complementary transverse second sealing element for the axial intake valve, borne by the rear end of the plunger,
a complementary transverse second sealing element for the axial equalizing valve, consisting of at least one portion of the rear face of the moving partition.
According to other features of the invention at least a first sealing element consists of a seal borne by an attached tubular bushing slideably mounted in the floating tubular element, the floating tubular element comprises, a tubular intermediate section, which is slideably mounted in an intermediate section of the piston which is roughly cylindrical and around a tubular bearing surface of the moving partition which slideably houses the plunger, a tubular front end section of a diameter greater than the diameter of the intermediate section, which is housed in a perforated front section of the piston lying where the piston and the moving partition meet, which internally houses a seal of which a front face forms the first sealing element for the equalizing valve and which is intended to collaborate with that portion of the rear face of the moving partition forming the second sealing element for the equalizing valve which is arranged radially on the outside of at least one drilling providing communication between the front chamber and the rear chamber, a tubular rear end section, of a diameter smaller than the diameter of the intermediate section, which internally houses the tubular bushing of which a transverse front end face bears a seal forming the first sealing element for the intake valve which is intended to collaborate with the second sealing element borne by the plunger, and of which a bore sealingly surrounds an axial inlet take duct in the piston communicating with the pressure source subjected to the pressure greater than the first pressure, the plunger is guided in a tubular bearing surface which extends axially from the rear face of the moving partition and the moving partition comprises a plurality of drillings distributed angularly through the transverse partition around the region when its tubular bearing surface and its rear face meet, a stepped face delimiting the tubular intermediate section and the tubular section of the tubular element has, bearing against it, the end of a return spring the other end of which bears against a stepped face of the tubular piston, a radial stop pin, of which the ends external to the piston are able to bear against the casing of the booster, passes through a drilling in the plunger, through two diametrically opposed slots in the tubular bearing surface of the moving partition, through two diametrically opposed slots in the element, and through two diametrically opposed slots in the piston, the diametrically opposed slots in the piston form part of the perforations in the piston, the intermediate section of the piston, of a determined diameter, includes the intake duct, of a diameter smaller than the determined diameter, with which it is integrally formed, and the intake duct is connected to the intermediate section by way of a transverse wall formed integrally and a front face of which forms the stepped face against which the return spring of the tubular element bears and the rear face of which forms a stepped face against which the return spring of the control rod bears, the transverse second sealing element for the axial intake valve is borne by a cup mounted tightly on the rear end of the cylindrical plunger and a transverse rear face of which extends opposite the seal forming the transverse first sealing element, the moving partition, the floating tubular element, the tubular bushing secured to the floating tubular element, the piston and the cup secured to the plunger are produced using cutting and pressing methods, a return spring is inserted axially into the floating tubular element between the plunger and the rear section of the tubular piston so as to exert a return force on the control rod, the axial intake valve is arranged at the end of an interior chamber of the tubular piston which chamber is formed in the rear section of the piston and communicates radially with the rear chamber, the transverse first sealing element for the axial intake valve surrounding an axial intake duct which is formed in the floating tubular element and which communicates with the external surroundings and the complementary transverse second element for sealing the axial intake valve being received with clearance in an axial drilling in the piston communicating with the interior chamber, the axial equalizing valve is arranged on the outside of the tubular piston and is arranged radially on the outside of at least one equalizing duct of the tubular piston placing the front chamber and the rear chamber in communication.
The floating tubular element comprises a tubular front section, slideably mounted on the rear section of the piston, which bears the first sealing element for the equalizing valve, and which is intended to collaborate with the second sealing element of the equalizing valve borne by the portion of the rear face of the front section of the piston, the first and second sealing elements for sealing the equalizing valve being arranged radially at least in part on the outside of at least one drilling providing communication between the front chamber and the rear chamber which passes through the front section of the piston; a tubular intermediate section which is slideably mounted on the rear section of the piston, and of which at least one longitudinal slot is formed radially in line with at least one longitudinal slot in the rear section of the piston which allows communication between the interior chamber of the piston and the rear chamber; a tubular rear section, of a diameter smaller than the diameter of the intermediate section, which forms the duct communicating with the external surroundings and which is slideably mounted on at least one tubular rear section of the plunger through which the control rod passes; and a transverse joining wall joining the intermediate and rear sections of the tubular element, and arranged more or less axially near the drilling in the end of the tubular rear section of the piston, comprises the first sealing element for the axial intake valve which is intended to collaborate with the second sealing element for the axial intake valve which is borne by the plunger and which is housed in the said end drilling of the tubular rear section of the piston.
The first sealing element for the axial intake valve consists of an annular part of the front face of the transverse wall joining the intermediate and rear sections of the tubular element; the complementary transverse second sealing element for the axial intake valve consists of an annular seal borne by an annular rear face of a cup carried by the plunger and which is housed with clearance in the end drilling of the chamber of the tubular piston; the first sealing element for the axial equalizing valve consists of an annular seal which is housed in a groove made in the front face of the tubular front end section of the tubular element; the complementary transverse second sealing element for the axial equalizing valve consists of an annular portion of the rear face delimiting the front and rear sections of the tubular piston.
The booster comprises a plurality of drillings which are angularly distributed in a uniform manner through the front section of the piston and which open into the rear face delimiting the front and rear sections of the tubular piston to form the equalizing ducts; the body of the piston has an internal axial bore which opens into the front face of the piston and into the interior chamber of the piston and which houses the end of the actuating rod of the master cylinder, the reaction disk, a sliding bushing, through which there passes a front section of the plunger, of which a step constitutes a front face coaxial with a feeler formed at the front end of the plunger to act upon the reaction disk.
A transverse wall, formed at the end of the internal axial bore, forms, on the one hand, an end stop for the step of the bushing and, on the opposite side receives the end of the return spring the other end of which rests against a front face of the cup of the plunger.
A stepped face delimiting the front section and the intermediate section of the tubular element has, bearing against it, the end of a return spring the other end of which bears against a stepped face of the casing.
The cup is inserted axially between the rear and front sections of the plunger with which it is integral while an annular seal is inserted between a tubular rear section of the casing and the tubular rear section of the floating tubular element, so as to provide a seal between the external surroundings and the rear chamber of the booster. The intermediate section of the floating tubular element has a plurality of longitudinal slots each arranged in line with longitudinal slots in the rear section of the piston, and the intermediate tubular section of the floating tubular element has at least one rotation-proofing finger which is slideably mounted in at least one of the said slots in the rear section of the piston, at least one element out of the moving partition, the floating tubular element, the intermediate bushing, the plunger and the piston, is produced using cutting and pressing methods, at least one element out of the moving partition, the floating tubular element, the intermediate bushing, the plunger and the piston, is made using a method of molding a plastic.
Other features and advantages of the invention will become apparent from reading the detailed description which follows, for an understanding of which reference will be made to the appended drawings.